SOME 35 YEARS AFTER THE FIRST COMPLETE DESCRIPTION OF PERIODIC LIMB MOVEMENT DISORDER (PLMD) BY LUGARESI,1 many drugs proved to be effective in improving symptoms,2,3,4 but the etiology of the disorder is still virtually unknown. PLMD may occur as a distinct disorder, in association with various drug treatments or other sleep disorders such as apnea5 or narcolepsy,6 and, very frequently, with r...